Survival of Human Neurofibroma in Immunodeficient Mice and Initial Results of Therapy With Pirfenidone

Plexiform neurofibroma: shedding light on the investigational agents in clinical trials

INTRODUCTION

Neurofibromatosis Type 1 (NF1) is an autosomal dominant genetic condition, which predisposes individuals to the development of plexiform neurofibromas (PN), benign nerve sheath tumors seen in 30-50% of patients with NF1. These tumors may cause significant pain and disfigurement or may compromise organ function. Given the morbidity associated with these tumors, therapeutic options for patients with NF1-related PN are necessary.

AREAS COVERED

We searched the www.clinicaltrials.gov database for 'plexiform neurofibroma.' This article summarizes completed and ongoing trials involving systemic therapies for PN.

EXPERT OPINION

Surgery is the mainstay treatment; however, complete resection is not possible in many cases. Numerous systemic therapies have been evaluated in patients with NF1, with MEK inhibitors (MEKi) showing the greatest efficacy for volumetric reduction and improvement in functional and patient-reported outcomes. The MEKi selumetinib is now FDA approved for the treatment of inoperable, symptomatic PN in pediatric NF1 patients. Questions remain regarding the use of this drug class in terms of when to initiate therapy, overall duration, reduced dosing schedules, and side effect management. Future studies are needed to fully understand the clinical application of MEKi and to evaluate other potential therapies through appropriate trial designs for this potentially devastating, manifestation in NF1.

Phase II trial of pirfenidone in children and young adults with neurofibromatosis type 1 and progressive plexiform neurofibromas

BACKGROUND

Pirfenidone, an oral anti-inflammatory, antifibrotic agent with activity in idiopathic pulmonary fibrosis, may mediate anti-tumor activity in neurofibromatosis type 1 (NF1) and plexiform neurofibromas (PN) by inhibition of fibroblast proliferation and collagen synthesis. The primary objective of this open label, single arm phase II trial was to evaluate the activity of pirfenidone in children and young adults with inoperable PN.

PROCEDURE

Patients (3-21 years) with NF1-related progressive PN received pirfenidone at the previously determined optimal dose (500 mg/m(2) orally, q8h) on a continuous dosing schedule (one cycle = 28 days). Volumetric MRI analysis was used to assess response. Progression was defined as ≥ 20% PN volume increase compared to baseline. Pirfenidone would be considered active if it doubled the median time to progression (TTP) compared to the TTP on the placebo arm of a phase II trial with the farnesyltransferase inhibitor tipifarnib, which used near identical eligibility criteria. Toxicities, objective response rate, and quality of life (QOL) also were evaluated.

RESULTS

Thirty-six patients were enrolled and tolerated pirfenidone well with intermittent nausea and vomiting as the most frequent toxicities. A dose reduction was required in only three patients. The median TTP for pirfenidone was 13.2 months compared to 10.6 months for the placebo control group from the tipifarnib trial (two-tailed P = 0.92; one-tailed P = 0.46). No objective responses were observed.

CONCLUSIONS

Pirfenidone was well tolerated, but did not demonstrate activity as defined in this trial and does not warrant further evaluation in children with NF1 and progressive PN.

Diffuse plexiform neurofibroma of the back: report of a case

Neurofibromatosis type 1 is an autosomal dominant disorder affecting the ras proto-oncogene. It is characterized by the overgrowth of nervous tissue and skin discoloration. While it is associated with a variety of phenotypic presentations, it is the plexiform variant that is particular concerning, as it can become extremely disfiguring and has a propensity for malignant degeneration. A case of a Pacific Islander with a large plexiform type 1 neurofibroma is presented. The patient was ultimately treated with surgical resection, negative pressure wound therapy, and split-thickness skin grafting with good results. A review of the literature concerning the diagnosis and treatment of neurofibromatosis is included.

Imatinib mesylate (Glivec) inhibits Schwann cell viability and reduces the size of human plexiform neurofibroma in a xenograft model

Plexiform neurofibromas (PNF), one of the major features of neurofibromatosis type 1 (NF1), are characterized by complex cellular composition and mostly slow but variable growth patterns. In this study, we examined the effect of imatinib mesylate, a receptor tyrosine kinase inhibitor, on PNF-derived Schwann cells and PNF tumour growth in vitro and in vivo. In vitro, PNF-derived primary Schwann cells express platelet-derived growth factors receptors (PDGFR) alpha and beta, both targets of imatinib, and cell viability was reduced by imatinib mesylate, with 50% inhibition concentration (IC(50)) of 10 microM. For in vivo studies, PNF tumour fragments xenografted onto the sciatic nerve of athymic nude mice were first characterized. The tumours persisted for at least 63 days and maintained typical characteristics of PNFs such as complex cellular composition, low proliferation rate and angiogenesis. A transient enlargement of the graft size was due to inflammation by host cells. Treatment with imatinib mesylate at a daily dose of 75 mg/kg for 4 weeks reduced the graft size by an average of 80% (n = 8), significantly different from the original sizes within the group and from sizes of the grafts in 11 untreated mice in the control group (P < 0.001). We demonstrated that grafting human PNF tumour fragments into nude mice provides an adequate in vivo model for drug testing. Our results provide in vivo and in vitro evidence for efficacy of imatinib mesylate for PNF.

Neurofibromatosis type 1 revisited

Neurofibromatosis type 1 (NF1) is an autosomal dominant condition with a worldwide incidence of approximately 1 per 2500 to 3000 individuals. Caused by a germ-line-inactivating mutation in the NF1 gene on chromosome 17, the disease is associated with increased morbidity and mortality. In the past several years, significant progress has been made in standardizing management of the major clinical features of neurofibromatosis type 1. Moreover, improved understanding of how the neurofibromatosis type 1 protein, neurofibromin, regulates cell growth recently provided insight into the pathogenesis of the disease and has led to the development of new therapies. In this review, we describe the clinical manifestations, recent molecular and genetic findings, and current and developing therapies for managing clinical problems associated with neurofibromatosis type 1.

Phase I trial of pirfenidone in children with neurofibromatosis 1 and plexiform neurofibromas

We aimed to define the dose of pirfenidone in children and adolescents with neurofibromatosis 1 and plexiform neurofibromas that is pharmacokinetically comparable to the active adult dose. Pirfenidone was administered orally on a continuous dosing schedule. The starting dose level was 250 mg/m2/dose. The second dose level (500 mg/m2/dose) corresponded to the adult dose that previously showed activity in sclerosing conditions. A dose was considered pharmacokinetically comparable if the drug exposure in children was <1 standard deviation below the drug exposure in adults treated with 800 mg three times a day. Pharmacokinetic sampling was performed for 24 hours after the first dose. Response to treatment was evaluated using automated volumetric magnetic resonance imaging analysis; quality of life was evaluated using the Impact of Pediatric Illness Scale. Sixteen patients were entered and evaluated for toxicity. Dose-limiting toxicities were observed in 2 of 12 patients receiving 500 mg/m2 three times a day. The plasma pharmacokinetics of pirfenidone were highly variable, but not age dependent. The second dose level was the pharmacokinetically comparable dose and is being used in an ongoing phase II trial of pirfenidone for children with neurofibromatosis 1 and progressive plexiform neurofibroma.